In general, in the case of the production of films or the like by using a T die, a thermoplastic resin fed from a hopper into an extruder is melted while being transported through an air-tight cylinder and the melted resin is extruded toward the T die. The molten resin is discharged through an elongated discharge port of the T die, whereby the desired films or the like are obtained.
The combinations of the extruders and the T dies are used to form cast films, sheets, laminated sheets and so on.
Of these plastic forming methods, as shown in FIGS. 1 and 2, the extrusion direction A of an extruder and a longitudinally extended discharge port 3 of a T die 2 are maintained mutually perpendicular. In the case of the production of laminated sheets, as shown in FIG. 3, the extrusion direction A of the extruder 1 is so determined as to be in parallel with the longitudinal direction of the discharge port 3 of the T die 2. The reasons why the relative position between the extruder 1 and the T die 2 is changed is as follows. In the case of the production of laminated sheets, film members to be laminated must be transported in the direction perpendicular to the discharge port 3 of the T die. When the extrusion direction A of the extruder 1 is maintained perpendicular to the discharge port 3 of the T die 2, the extruder interrupts the transportation of a film member to be laminated cannot be transported in the direction perpendicular to the discharge port 3 of the T die 2.
Each of the production methods described above can produce not only film members each consisting of a single layer and laminates each consisting of a single layer but also film members each consisting of a plurality of layers and laminates each consisting of also a plurality of layers. When the plastic products each consisting of a plurality of layers, not only the quality of the produced film members and the like can be improved but also the production costs can be reduced to a minimum.
In the case of the production of film members each consisting of a plurality of layers, the molten resin jets extruded from a plurality of extruders 1 are fed into the single T die in such a way that the mixture of molten resins within the T die or after discharged from the discharge port 3 can be prevented and each layer is overlaid one upon the other, whereby the film members each consisting of a plurality of different resin layers can be produced.
More particularly, in the case of the production of film members each consisting of a plurality of different resin layers, a required number of extruders 1 are disposed at their respective suitable positions depending upon an object to be formed. Thereafter the extrusion port of each extruder 1 is communicated through an adapter with its corresponding molten resin jet input port of the T die so that a plurality of different molten resin jets are fed into the T die 2 through the molten resin feed passages defined within the adapters. As typically shown in FIGS. 4(a), (b) and (c), various types of T dies are used to form sheets each consisting of two layers. In each type, two inlet ports 4a and 4b of the T die are communicated through specially designed and constructed adapters 5a and 5b with two extruders (not shown). The molten resin jets fed to the inlet ports 4a and 4b flow through feed passage 6a and 6b, respectively, and after they are joined, they flow into a manifold 7 extended in the longitudinal direction of the T die 2 (in the direction perpendicular to FIG. 4) and then a feed passage with a small cross section 8. Thereafter they are discharged through the discharge port 3 whose cross section is defined by a stationary lip 9 and a movable lip 10 as a two-layer film member in which the thickness of each layer is uniform in the widthwise direction. In the case of the T die 2 shown in FIG. 4(b), the molten resin jets fed to the inlet ports 4a and 4b flow independent feed passages 6a and 6b and manifolds 7a and 7b in the order named and are united within a feed passage 8 and then are discharged through the discharge port 3 as a two-layer film. In the case of the T die as shown in FIG. 4(c), the molten resin jets fed to the inlet ports 4a and 4b flow through the independent feed passages 6a and 6b, manifolds 7a and 7b and feed passages 8a and 8b in the order named are discharged as a single layer film member through each of independent discharge ports 3. Thereafter the discharged single layer film members are combined into a two-layer film member.
In general, in the case of the production of plastic articles using the extruders 1 and the T die, in order to improve the efficiency of operation, at least one extruder 1 is used and disposed the position as shown in FIG. 1 or 2 so as to form cast films or sheets. Furthermore the position of the extruder 1 is changed as shown in FIG. 3 to produce laminates.
However, even though it is easy to switch the position of the T die 2 through 90.degree. with respect to the extrusion machine 1, in the case of the projection of plastic articles each consisting of a plurality of layers, the positions of a plurality of molten resin jets inlet ports are considerably changed due to the switching of the relative position of the T die with respect to the extruder 1; that is, it is difficult to switch the positions of the inlet ports of the T die 2. In other words, in the case of the formation of plastic articles each consisting of a plurality of different resin layers, in order to switch the position of the T die 2, adapters adapted to communicate the discharge ports of the extruders with their corresponding inlet ports of the T die must be prepared and the operation for exchanging the adapters must be carried out. Especially in the case of the production of plastic articles each consisting of more than three layers, the inlet ports of the T die 2 and the adapters are increased in number. This causes a considerably troublesome problem.
In the case of winding a multi-layer film member around a take-up roll, in some cases it happens that the inward and outward resin layers must be reversed. In this case, in the conventional methods and apparatuses, the positions for communicating each extruder and the T die must be changed, which is very cumbersome.
Furthermore in the conventional production of multi-layer film members, they must be so formed that the thickness of each layer becomes uniform in the widthwise direction. And the film members each having a plurality of resin layers which are different in thickness are rejected as defective articles.
However, in the case of film members each having a plurality of different resin layers, except the fact that the thickness of each resin layer is made uniform in the widthwise direction, it was found out that they can be applied in various fields.